1. Field of the Invention
The present invention relates to an opto-magnetic recording apparatus for performing recording, reproduction, and erasure of information with respect to an opto-magnetic recording medium by cooperation of a light beam and a magnetic field.
2. Related Background Art
The above opto-magnetic recording media include disk- and card-like media. In the following description, a disk-like opto-magnetic recording medium (to be referred to as an opto-magnetic disk, hereinafter) will be exemplified.
In an opto-magnetic disk, a magnetic thin film having an axis of easy magnetization perpendicular to the film surface is formed on a substrate. Information can be recorded in accordance with a change in magnetization direction of the magnetic thin film. In the recording mode, magnetization of the magnetic thin film is aligned in one direction, and the magnetic thin film is irradiated with a laser beam digitally modulated with an information signal, while a bias magnetic field is applied to the disk in a direction opposite to the magnetization direction. A temperature of a portion irradiated with the laser beam is increased and thus, a coersive force thereof is decreased. The magnetic thin film is magnetized in a direction in the opposite direction by the bias magnetic field, thereby forming a magnetization pattern according to the information. Information recorded in the opto-magnetic disk in this manner can be optically readout upon radiation of a low-power nonmodulated beam on the medium according to a known magneto-optical effect. In addition, information can be erased when a magnetic field, having a direction opposite to the bias magnetic field applied in the recording mode, is applied to the magnetic thin film.
FIG. 1 is a schematic view showing a conventional opto-magnetic recording apparatus using such an opto-magnetic disk. An upper cover 42 is mounted on a frame 41 of the apparatus and is opened/closed when an opto-magnetic disk 43 is loaded/unloaded. The opto-magnetic disk 43 is clamped on a turntable 44 by a clamper 48 and is rotated by a spindle motor arranged in a head frame 45. An optical head 46 is radially moved along a guide 49. The opto-magnetic disk 43 is irradiated with a light beam from the head 46 to record information therein. A magnet 47 is integrally arranged with the optical head 46 to apply a bias magnetic field to the disk 43 and is radially moved together with the optical head 46. With the above arrangement, although the size of the magnet 47 itself is small, the optical head 46 as a movable member becomes bulky, and high-speed access cannot be performed.
FIG. 2 is a schematic view showing another conventional opto-magnetic recording apparatus. The same reference numerals as in FIG. 1 denote the same parts in FIG. 2, and a detailed description thereof will be omitted. In this example, a bias magnet 47 is large enough to cover the radial recording area of an opto-magnetic disk 43 and is fixed on an upper cover 42 of the apparatus. The bias magnet 47 comes close to the opto-magnetic disk 43, as indicated by a broken line, when the upper cover 42 is closed. This example has a simple structure, but is applicable only to an apparatus with an upper cover. In this case, the loading/unloading aspect of such a medium is very important to synthesized with other information equipment. In particular, the height of the installation space is limited and the above-mentioned apparatus with an upper cover cannot be used when media other than the magnetic disk are utilized.
The opto-magnetic recording apparatus as described above is described, e.g., in Japanese Patent Laid-Open No. 147949/1985.